The document WO 2008/119785 A1 discloses a magnetic actuator unit for a circuit-breaker having a first electrical coil, a second electrical coil and an armature arranged to be moveable between the first and second end position by means of said electrical coils. The electrical coils are arranged in an anti-series connection, and both coils are energized simultaneously for effectuating the movement of the armature between the two end positions. This technical solution provides a bistable actuating arrangement and two electrical coils are necessary therefore.
The document GB 1,454,354 discloses another magnetic actuator unit with only one electrical coil for moving the armature to one of the end positions. Additionally, an integrated opening spring is provided to generate force in the opposite direction. The opening spring is arranged inside the magnetic actuator unit surrounding the armature, which is also accommodated mostly inside the magnetic actuator unit in order to keep the volume of the arrangement as small as possible. However, the arrangement of the specific parts, especially the yoke surrounding the whole magnetic actuator unit, is not able to generate a high actuating force. For operation of modern medium voltage-circuit-breakers a higher force is used to operate the moving electrical contact.